adds a note for installment (#5)

Author: ringabout

src/htmlparser.nim

@@ -7,6 +7,8 @@
 #    distribution, for details about the copyright.
 #
 
+## .. note:: In order to use this module, run `nimble install htmlparser`.
+##
 ## **NOTE**: The behaviour might change in future versions as it is not
 ## clear what "*wild* HTML the real world uses" really implies.
 ##
@@ -2073,4 +2075,4 @@ when not defined(testing) and isMainModule:
     f.write($x)
     f.close()
   else:
-    quit("cannot write test.txt")
+    quit("cannot write test.txt")